Well, I made the list using the two sites below, one being a book with some Eriobotrya species and their distribution in China (not neighboring countries) and the other being a USDA zone map of China. I couldn't find any ready-to-use zone information for most species (other than japonica and deflexa), probably because those species aren't being cultivated outside their native range.
If you look at the uppermost left spot for E. fragrans in the book and compare it to the zone map, that area is supposedly zone 5. The rest of its native distribution area is zone 8+ though, so I didn't write the zones inbetween.
Established E. japonica trees are hardy to about 12°F (-11°C), so zone 8a. According to the paper from my first post, E. fragrans is hardier than japonica. Probably not zone 5 though.
Regarding fruit in colder climates, at least E. japonica, the regular loquat, has an unusual flowering habit in that they flower in fall and bear fruit in spring. So in any area that has temperatures below about 27°F (-3°C) in winter, fruit is unlikely. But you can still grow the plants themselves, e.g. as evergreen ornamental. In the best case, there would be a hardier relative of japonica that flowers in spring and bears edible fruits in fall. But I would be happy with anything that is a bit hardier than japonica, so that I could attempt growing it in zone 7 with protection.
The paper mentions quince rootstock on page 11, stating that is is mostly used for its dwarfing effects in commercial fruit production but that it isn't compatible with all varieties and leads to zinc deficiency in the plant. Do you think it would make the trees hardier? Aren't they more resistant to the cold on their own roots?
Also, thanks for the suggestions, I'll have to look up E. hookeriana and E. petiolata